1. Field of the Invention
The present invention relates in general to a saw blade having a rim embedded with hard particles for cutting hard materials, such as concrete, masonry, tile, granite and the like. More specifically, the invention relates to a cutting blade that includes an impact load prevention layer therein.
2. Description of the Related Art
In the past, circular saw blades for cutting soft materials, such as wood, having teeth about the perimeter have been proposed which include dampening means (such as in U.S. Pat. Nos. 2,563,559, 4,232,580, and 4,240,315). These conventional saw blades adjust the natural resonance frequency of the blade to dampen blade vibration. Towards this end, the '599 patent fills radial slots within the blades steel core with a soft metal and a reinforcing rib. The '315 patent divides the blade into sectors via slots extending from the outer periphery of the blade towards the hub. Each slot is a different length to provide adjoining sectors with different natural frequencies. The '260 patent forms a saw blade with two circular annular chambers along opposite sides thereof. Each chamber includes a dampening layer made of a resin adhesive which is highly elastic.
However, these blades were ineffective for cutting extremely hard materials, such as concrete, masonry, tile, granite and the like. Hence, alternatively blades were proposed with extremely hard abrasive outer rims mounted upon a steel core to cut these materials. The outer rim includes particles, such as diamond particles, tungsten carbide, polycrystalline diamonds, and the like, mixed within a bonding agent. The mixture is molded to form a hardened outer rim. The hard particles extend outward about the perimeter of the blade and, during cutting, these particles cause the blade to shake and quiver in a radial direction, thereby causing the blade to bounce against the surface being cut. This radially directed reverberation is commonly referred to as "chatter." Chatter increases the noise level produced during the cutting operation. Additionally, saw blades formed with hardened outer rims are typically powered with combustion engines, such as gasoline-powered engines. The combustion engines produce additional vibrations which are transmitted along the drive shaft to the saw blade, thereby precipitating chatter.
When the blade radially bounces against the surface to be cut, the hardened particles projecting from the outer rim experience large instantaneous impact loads. These hard materials are typically, extremely brittle. Consequently, the out most portion of each hard particle tends to shear off during impact loads. Thus, these types of saw blades tend to wear quickly, unless the outer rim of the saw blade is maintained in constant contact with the surface to be cut (i.e., a constant cutting mode).
However, heretofore no satisfactory method has been proposed for eliminating impact loading within a saw blade containing an outer rim embedded with hard particles. Nor do conventional saw blades satisfactorily reduce the noise level. Moveover, conventional systems typically utilize a steel core since steel is easily bonded to the outer rim. However, steel exhibits limited heat dissipating characteristics. The saw blade size dictates its ability to dissipate heat without this heat being transmitted to the arbor shaft. Typically, a proportional relationship exists between the size of the saw blade and the horsepower of an engine which is usable therewith.
In a somewhat corollary field, grinding drums have been proposed for minimizing vibration (such as in U.S. Pat. Nos. 4,549,372 and 5,083,839).
The system of the '839 patent, as proposed by a co-inventor of the subject invention, is directed to a grinding drum for grooving or grinding pavement. The drum of the '839 patent comprises an inner cylindrical core having a plurality of sleeves disposed thereon. The inner core is surrounded by an intermediate cylindrical sleeve which absorbs shocks, jars, and harmonic vibrations imparted to the rotary drum during use. The intermediate sleeve is surrounded by an outer sleeve which serves as the mounting surface for grooving segments. The inner core is formed of metal, the intermediate sleeve is formed of an impact resistant material, and the outer sleeve is formed of steel. A plurality of grooving segments are disposed about the outer sleeve, each grooving segment comprising a plurality of grooving surfaces disposed in parallel rows. The grooving drum of the '839 patent forms grooves approximately 1/8" wide and 3/16" deep, with a lateral distance of approximately 3/4" between each groove.
The system of the '372 patent discloses a grinding drum with a hub mounted on an abrasive rim. The rim is resiliently depressible radially inward toward the hub during a grinding operation. In one embodiment, the hub is surrounded by a resilient ring, formed of rubber or honeycombed metal. The resilient ring is surrounded by a thin flexible aluminum hoop. When the rim is depressed it loses its circular shape.
A cutting wheel has been proposed (U.S. Pat. No. 3,342,530) for a mining machine which includes an easily replaceable cutter bearing rim. The '530 patent includes a cutting wheel having an integral shaft and core flange. The core flange projects outward and forms an inner rim element immediately adjacent an outer rim element. A solid resilient substance is formed between the inner and outer rim elements to cushion or absorb a portion of the cutting strain, such as when the cutting bit encounters material within a coal vein which is harder than the coal being cut by the tool.
However, it has been impossible to implement the vibration dampening techniques of the '839 patent, '372 patent and '530 patent with a cutting wheel having hardened particles embedded in-an outer rim thereof. Cutting wheels of this type experience forces uncharacteristic of grinding wheels and mining tools. Further, cutting wheels of this type carry design restraints which need not be addressed with grinding wheels and mining tools.
For instance, in the systems of the '839 and '372 patents, the vibration dampening layer is formed with a width equal tot or greater than, that of the grinding surface. This is necessary to provide sufficient support for the grinding surface and to withstand the opposed forces exerted by the core and the grinding surface. However, a cutting surface of diamond embedded cutting wheel is formed with a substantially lesser width. Thus, a resilient pad equal in width to a diamond embedded cutting surface would be unable to support the cutting rim, nor could it withstand the circumferential and lateral forces between the drive shaft and the cutting rim.
Also, the vibration dampening layers of the '839, '372 and '530 patents are positioned immediately adjacent the grinding surface. However, these dampening layers would create complications within a cutting wheel since the dampening layer would necessarily pass through the cut. Thus, when cutting hard materials such as concrete and masonry, the width of the dampening layer must be smaller than the width of the cut. The systems for grinding wheels are not limited by a similar design restriction since the body of the grinding wheel never passes through a cut within the surface being ground. The vibration dampening layers of these conventional systems are not designed to withstand the lateral prying forces experienced by a diamond embedded cutting wheel. Throughout a grinding operation, grinding wheels rest against the outer surface of the material being machined. Hence, the grinding surface does not overly resist prying forces applied by the user to turn the tool. Nor do the sides of the grinding wheel experience significant contact and lateral forces from the cutting surface.
Further, the dampening layer of the '372 patent is formed to allow the grinding surface to distort to an oval, or non-circular, shape during a grinding operation. However, if a cutting wheel were so deformed, it would not cut properly. Moreover, the systems of the '839 and '372 patents need not be as concerned with impact loading since grinders offer a much larger working surface area, over which the impact load is distributed. Grinders do not focus the energy of the grinder along a single narrow path. Divergently, cutting wheels offer a very small cutting area in which the cutting energy is focused. Thus, impact loads are quite focused within this area.
Finally, a grinding drum is much larger than a cutting wheel, and thus a grinding drum is more capable of dissipating heat. Accordingly, designers of grinding drums need not be as critical of the heat dissipating characteristics of the end design.
The need remains in the present field for an improved blade design to address the problems and drawbacks heretofore experienced. The primary objective of this invention is to meet this need.